The City of Los Angeles has standards for parkway landscaping that are being enforced. A booklet with lots of valuable information about landscape alternative and the legal process is available from the Engineering Division at http://bss.lacity.org/Engineering/pdfs/Residential_Parkway_Landscaping_Guidelines_halflayout.pdf. For street tree information please see http://bss.lacity.org/UrbanForestry/index_soyouwanttoplant.htm. Permits may be applied for at the Bureau of Street Services: http://bsspermits.lacity.org/